1. Field of the Invention
This invention relates broadly to medical canalicular inserts. More particularly, this invention relates to plugs which are placed into the punctal opening of the lacrimal duct to prevent lacrimal fluid from flowing through the lacrimal duct.
2. State of the Art
A variety of eye problems are related to an insufficient volume of tears on the surface of the eyes. The most common is keratoconjunctivitis sicca, also known as dry eyes. Contact lens problems are also often provoked by a lack of tear volume. A common cause for the insufficient tear volume is the drainage of tear fluid through the punctal opening of the nasal lacrimal duct and into the nasal passage, thereby removing the fluid from where it is needed at the eye surface. Furthermore, drainage of tear fluid through the nasal lacrimal duct into the nasal passage is believed to be the cause or associated with several additional problems such as post nasal drip, sinusitis, allergies, headaches, and snoring.
A number of methods for closing the punctual opening have been used to prevent drainage of tears through the nasal lacrimal duct, including suturing, laser sealing, and plugging. Plugging with a punctum plug is the least severe solution, is relatively inexpensive, and is being performed with increasing frequency.
Referring to prior art FIG. 1, a punctum plug 10 typically is an elongate member having a proximal head 12, a large distal body 14 for occluding the lacrimal duct 16, and a narrow rigid shaft 18 therebetween. The plug is usually provided with a proximal axial conduit 20 for receiving an cylindrical insertion tool. In the punctum plug insertion procedure, an insertion tool is positioned into the plug, the body of the plug is directed at the punctal opening 22 of the lacrimal duct 16, and force is applied to the insertion tool to move the body of the plug through the punctal opening and into the vertical puncta 24 and lacrimal duct 16. Once the plug is in the vertical puncta and lacrimal duct, the insertion tool is removed. The plug is fully inserted when the head seats against the tissue at the punctal opening and the body seats within the lacrimal duct so as to block the passage of tear fluid and thereby retain tear fluid at the surface of the eye.
It has been found that prior art punctum plugs, while providing some benefit often do not provide satisfactory occlusion of the lacrimal duct. Tear fluid tends to flow through the interstices between the body of the plug and the tissue of the vertical puncta of the nasal lacrimal duct. One proposed prior art solution of this problem has been to provide an enlarged distal body to the plug. However, this poses two problems. First, the larger distal body is difficult to insert into the relatively small punctal opening. Second, some persons have relatively short vertical puncta. As a result, the body of the plug, rather than resting within the vertical puncta, is forced against the duct tissue 26 where the vertical puncta meets the lacrimal duct. This urges the plug upwards and can cause the plug to be unintentionally dislodged.
Another problem of the prior art plugs is that, in some instances, the plugs cannot be easily extricated from the punctum. Occasionally, the tissue of the vertical puncta closes in around the shaft of the plug. As a result, when lifting force is applied to the head of a well-seated plug to lift the plug out of the puncta, the plug tends to break at the shaft. The plug is thereby decapitated leaving the body and a portion of the shaft behind, which cannot be removed without a more severely invasive procedure.